Processes of treating magnesiumbase castings and improved magnesium-base alloys produced thereby



Patented July 26, 1949 enocassjas or. 'raEATiNo nasi: casamos AND.IMraovlin.lyiatimn-4v SIUMvBasc ALLQXS econoom incitent Edward .LVargto, Warrensville Heights, Qhio, as` signor to The Wellman Bronzeand;Aiunrninum` Gemeente. Moreland, ohio, annotations ct NoDrawing.Application Deeem SeralNo. 65,7441" seriales-a.

2e @was 01- leans).

The invention relates. to. alloys, and: particularly to alloys having amagnesium` base.

ofA treating magnesium-base` castings to produce the improved alloys. 5stated, little. difficulty has` been, encountered in This application`on said inventionis a continumeetingthaplfopenties specied.f.or.ANM-36,the ation-in-part application of my pending applica.-diifverenceof,-2000zp.s.i.inltensilestrength which is tion Serial No.586,024,1iled. March B1, 194,5, now specified for the aged condition.over the` heatedA abandoned, on Magnesium-.base alloys and procconditionhasi not been maintainable. On the essof treating thesame, and mypending applica- 1o contrary, the. ane-ragey tensile strength found` ina tion SerialI No. 18,858, ligledr April 3, 1948., now` large numberoifoundry-produced composition abandoned, on Processes oftreatingmagnesium- A magnesium` alloys tested was some 500`p.s.i. base castingsand improved magnesium-.baseA allower-for.the.aged, condition than forthe heated loys produced thereby. condition onlyi This average for theaged" con- Primarily, the invention comprises improveeition was about39,000; whereas, the expected ments in aging magnesium-.base castings bydifierentialshould have produced an average ofl continuous heating atstepped temperatures about:41',500lp.s.i, whereby the ultimate`strength, elongation, yield It. has been found that testA bars castunder strength, and hardness are improved. close laboratorycontrolyielda tensile strength of Insofar as I am informed, known processes ofapproximately k1,000p.s.i1. andan elongation of heat-treatingmagnesium-base alloy castings substantiallye`161% forithe;solution-heat-treated consists in giving them a solution heattreatcondition, while. the tensile strength is approxiinent immediatelyfollowed by an air quenchrnatelye42,-500lp.s.i. andthe elongation 7%after ing, and then aging them by heating at about the-bar hadfbeenagedfonsixteen hours at 350 F. 350 F. for about sixteen 16) hours, andthen re- 25 However, lessrieidly controlled castings of test moving themfrom the heat treatment furnace bars in. commercial practice yield: atensile anclletting themair-.cool at room temperature. strength ofapproximately-40,000 psi. for the it has longbeen well recognizedin`commercial heet leetedf metal; andf39l000 D-S-- for the .metal practicethat, although a difference of 2000 p.s.i. agedfor Sixteen-hours'ot35-0F1, With- IleSlUeC'LVe in tensile strength between thesolution-heatelongatorls Off approximately 14o11d 5%j `This treated andthe solution-heat-treated and aged disceparloy` between tensile StrenthSvof the conditions of the commercial magnesium casting laboratoryspecimenanclf the commercial pracalloys such as A263 and AZ92 isindicated by the tice Specimen is. explained byttljie respectivedifspecications to be feasible, there is a persistentferenGeS-inelongaton. ThetWoheoii treatments, inability to maintain thisdifference. However, the solution heattreatmentA and the aging theincrease in yield strength and the decrease heat. treatment, elleChefreioteljzedbywell defined in elongation do correspond in commercialpracstress-strain. curves, and-- they cast quality 0f a tice to thoseofthe specifications. The commer- @est bei@ does not affect the shape ofthe curve cial magnesium castingalloys A263 and A292 butti011157detellflflllesly its terminal point. This are, respectively, thosein which aluminum conio elmrlalpoint has coordinateswhich representminutes about 6 and 9%, Zincabout 3 and 2%, theelongationandthetensilestrength. Therewith `from 0.15 to 0.20% maganese, and traces fore, theelongationof 16%in the laboratory bars of other foreign elements such assilicon, iron, oo1\l^eS-l&0IlC-S-` t0 elJ-Si- 0f` 413000, and theCometc., the remainder of the casting alloy being marcial elongationof,z 14%- produces-a` ns-iof magnesium. Manganese is added to al1 com-45 401,000, Whichu is on1y`1000 poiloWer than the mereial magnesiumalloys to im'ppove the cor.. laboratory value. the laboratory.- bar, inthe rosion resistance and is, therefore, disregarded aged Condition,theelongatiorlofe't; determines herein, a tensile strength .of-:42,500 psci., and for the com- Because in commercial practice the specifiedinertialv bell', the elongation of 5% Produces a properties arerelatively low, there has been entensile. strength of.3'9,000.p.s.i.,which is3500 p.s.i. counteredlittle diiiiculty nmeeting the properlowerthan the` laboratory: Value. Therefore, Cleties `specified for AN-M-B,in either the heatfectstin or` a decrease in the.- casting qualityretreated or the.heat.-treated and `aged condition. duces thetensilestrengthof the agedcondition AN-M-e is an Army-Navy aeronautical.speciconsiderably..more.,V than', that of=li the solutionfication, onetype of which known as composi.- heat-.treated condition! However, theallowance The; in". vention also includes improvements. in processes`tion, fAt cor-nainsA4 substantially, 6%. aluminum,

zinc, and; 0.20% manganese, with traces of.

other foreign. elements; It-` is. the. specication heneinbeiore;referred. to. as AZ63. Although, as

made by the specifications in commercial practice for an inferiorcasting is considerably larger for the heat-treated condition than forthe condition both heat-treated and aged. It is evident that thesespecincations should set aV minimum tensile Y Vstrength of the agedcondition at an equal or smaller value than that of thesolution-heattreated condition. The stepped aging treatment hereinpresented eliminates this necessity, and also produces improvedcharacteristics of the resultant casting alloys. It also'eiects a greatYsaving in total heat-treatment time. i

I have discovered that the inability to maintainj the 200@ p. s. i.difference in tensile strength bei; tween the two conditions of thealloy is causedj by a prematureltermination in the stress-strainY curveresulting from casting defects. 'IY-:his premature termination resultsin a greater loss in' the tensile strength for the heat treated and agedcondition casting than for the casting which hasVY been heat treatedonly. Therefore, the invention disclosed herein-comprises an fimprovedaging treatment for which the curve indicating the stress-strain is notprematurely'terminat'ed, such improved aging treatment being effectiveto improve the characteristics of the resultant alloy such as itstensile strength, yield strength, elonga tion, and hardness. Y

Occasional'diiculties with temperature control when producing the`composition A magnesium alloy resulted ir certain heats being subjectedto a stepped aging suchV as at 250 F. for three hoursand at 35 F. forthirteen hours. The product o-.these heats hada strength value greaterthan that resulting from the normal heating at a uniform temperature of350 F. over the same totalgime. Therefore, the whole production wastentatively subjected to a stepped aging treatment. It was found thatthetensile strength was decidedly' higher than either thesolution-heat-treated product or the normally aged product. Comparisonof test bars subjected to solution heat treatment vonly showed-identicalproperties; whereas, comparison of the aged test bars showed theincreased strength values. Therefore, the benefitswere attributable tothe differential aging treatment. f-

Primarily, the improvements consist in a stepped aging treatmenthavingdifferent temperature and time factors. For instance, it has beenascertained by laboratory tests that an aging treatment which utilizesvarious times of heating at two temperatures with a total timerequal tothat of the regular commercial practice at one temperature results ingacombination of tensile strength, per cent elongation, and yield strengthwhich is superior to that obtained in regular commercial practice. Also,it has been ascertained that an aging treatment which utilizes twoperiods of heating time, employing a higher temperature.

in the second period of the agingtreatment,results in properties whichare equal to those obtained @in commercial practice, even when the totaltime of the improved?Y stepped aging treatment isY only about:25% of thetotal time required by commer-f cial practice at one temperature.

A part of the improvements-presented herein consists in aging themagnesium-base castings, after the solution heat treatment including theair quenching, by heating them for about `three (3) hours at 250 F., :1-15, and then continuing the heating for about thirteen (13). hours at350 F., +30-10. The castings are then removed irom the heat treatmentfurnace and air cooled at and to room temperature. This im-A Y then at atemperature of from about 350 F. to

about 400 F., during which heating the aging time at the lowertemperature does not exceed one-half theltotal aging time.W Preferably,the total aging time is aboutfour hours, during which the heating jatthe lower temperature is from about one to about one and one-half hours,and the heating at the higher temperature is Yfrom about two andone-half toabout three hours.

All of the aging treatments comprehended by thelpart of the improvementslast-described produce an improved 'combination of properties inthe'resultant alloys over those of similar alloys heated for the wholeperiod at about 350 F. for about sixteen (15) hours, the particularproperties improved being hereinafter designated for certain of the2stage heating procedures which will be hereinafter described.

Reference to the results which have been obtained by a 2-stageaging'treatment of about three (3) hours at 250F., m15, and thenacontinued heating for about thirteen (13) hours at 350 F., +3010, forwhich results there have been treated a magnesium-base castingcontaining 6% aluminum,l3% zinc, about 0.15% inanganese, and the balancemagnesium; and also a casting containing 9% aluminum, 21% zinc, 015%manganese, and the balance magnesium, shows that the ultimate strengthby the improved 2-stage procedure had been increased by about 2000 p. s.i. over the ultimate strength produced in test-pieces from the samecasting operation by an aging thereof for sixteen hours at 350 F.; andthat the hardness, bythe Brinell table, had been increased about fourV(4) hardness numbers, and the percentage of elongation in 2 gaugelength test-pieces had been increased about 1.5.

The temperatureV at which the iirst phase of the aging operation isYeiiected, over a heating period of about three hours, is quitecritical, viz., 250 F., as stated,.but I have ascertained that a rangeof temperature within i;15 of 250'F. produces improved ultimatestrength,`hardness, and elongation characteristics. The temperature atwhich the second'phase of the aging operation is effected,

Y 017er a period of about thirteen (13) hours, viz.,

350 F., islalso quite critical, having, however, a permissible rangewithinV Which the improved results are obtained, this range being +30and -l0 from 350 i Y In MgAlZn castings, as also in-other magnesium-basecastings, there will be traces of foreign elements other than thosewhich-"enter into the compounds which are found concentrated in thealloys and which precipitate during the aging yoperation in pearliticstructures, :such asc-manganese, silicon, iron, nickel, etc.1 Inasmuchas these other elements are not present in the pearlitic structuresprecipitated by the aging operation and,Y thereforefhave no effect inthe production of the improved' characteristics, according to my theoryof the rproduction of the latter, no further reference to such otherelements is made herein.

The results of the second part ofmy improve- Y ments which involve ashorter period of total aging time, viz., from about four to about eighthours at initial temperatures of from about 225 F. to about 275 F., andsecond heating temperatures of from about 350 F. to 400 F., wereobtained by aging, and noting the improved results, the Army-NavyAeronautical Specification AN- M-BS, known as composition A. This is thecomposition hereinbefore 'referred to as containing substantiallyaluminum, 3% zinc, and 0.15% manganese, with traces of other foreignelements, the balance being magnesium. This specificais referred to asA253 and its maximum and minimum limits are: aluminum `,5.3 `to 6.7%,zinc 2.5 `to 3.5%, manganese 0.15% minimum, and silicon 0.30% maximum,the balance being magnesium.

This specication covers the most common heattreated magnesium castingalloy. However, the

improvements are abplicableto and the improved characteristics obtained`from the various magnesium casting alloys containing from 6 to 9%aluminum, 3 to '2% zinc, 0.15 to 0.20% manganese, with traces ofsilicon, iroL etc., the balance ybeing magnesium.

Various closely-controlled laboratory tests of the conventionalagin-gtreatment have been conducted for vdifferent total times, anddifferent temperatures. Conventional aging has been tested for variousperiods upto 500 hours and at temperatures from 250?. to 400 F. For eachvariation of the aging treatment .many specimens of the product havebeen tested for yield strength, tensile strength, `elongation (per 2inches), and Brineli hardness. of the results withresults of similartests using the stepped `aging treatment produced a better combinationof properties 4by the stepped aging treatment using differenttemperatures than by the conventional aging treatment over the whole .-g

period of time at a :single temperature. it was also ascertained thatfor the given aging temperatures and total time there `results `from thestepped aging an almost constant or slightly increased yield strengthand tensile strength and an elongation from 1 to 2% above the valuesobtained by aging for the entire period at the higher temperature. Thus,stepped aging temperatures of 250 F. and 350 F. over the usual totalcommercial time of sixteen hours has been tried; also, a total agingtime of eight hours at 250 F. and 400 F.; and a total agingtime of fourhours at 250 F. and 400 F. The first aging time of 250 F. was tried ineach series from zero hours to the total hours. For each series oftests, a better combinationof properties than was obtainable by a single`temperature aging was obtained by stepped aging in which a fraction ofthe aging time is consumed at 250 F. However, it was further ascertainedthat a reduction in yield strength, whichcannot be tolerated, made itnecessary `that the lower temperature aging time, i. e., the agingtimeat which lsubstantially 250 F. is utilized, `whilea .substantialportion of the entire aging period, should not exceed onehalf Of thetotal time. Also, itis knownfthat the aged condition improves with lower`temperatures but a second-stage temperatureimaterially below 350 F. isimpracticable in standard practice because of `the great length .of timenecessary `for satisfactory aging. Apracticable feasible aging timeshould not exceed twenty-four'hours.

It has been further ascertained-.that `the lowest `combination'oftemperatures utilized, i. Ve., 250

and `350" F., for atOtnl.lagingperiodof nsix- For every test, acomparison teen hours, yields the best combination of Aprop-- ertiesexcept that a total aging time of fourhours with the use of temperaturesof 250 F. and 400 F. yields an equal improvement or possibly slightlylarger. For this stepped aging use of 250 F. and 400 F., a rst agingtreatment of 250 F. for one and one-half hours, and a second agingtreatment of 400 F. for two and one-half hours .is indicated, resulting,y'as compared with conventional aging at 350 F. for sixteen hours, in atensile strength only slightly lower, in markedly increased elongation,and in an insignificant decrease (readily tolerated) in yield strength.However, an aging Iperiod of eight hours, using 250 F. and 400 F.,yields properties only slightly improved over those obtainable by lanaging 'heat of 400 lor the entire eight hours, indicating that-overaging is a deleterious factor, markedly more so than underaging. Itis further yascertained that an increase of the time required for agingto obtain a maximum tensile strength produces a considerablylessfavorable combination of strength and elongation than does underaging,Furthermore, the complete aging time decreases with increasingtemperature but the properties simultaneously decrease.

Application to commercial practice of the stepped aging treatmentabove-mentioned has given even better results than those obtained bylaboratory tests of the improved stepped aging treatment.

A large number of bars of commercial production have been tested over a4-hour aging period consisting of one hour at 250 F, and three hours at400 F. This stepped aging treatment produced properties distinctlysuperior to commercial procedure of sixteen hours Aat 350 F. The tensilestrength was equivalent, and the :yield strength yand elongation werehigher, despite the reduction of in total aging time.

The results indicate that otherpromising combinations of temperaturesfor stepped Iaging are 250 F. and 375 F., 275 F. and 375 F., and 225 F.and 400 F., utilized for a total aging time of about `four hours, inwhich the aging time at the lower temperature does not exceed one-halfthe total aging time. Results obtained indicate that the bestcombination of properties is obtained 4by a total aging time ofapproximately four hours, one and one-half hours at about 250 F., andtwoand one-half hours at about 400 F.

My theory of the cause of .the improved characteristics obtained by theimproved 2-stage-aging treatment above-described is as follows:

It is known that, in the cast condition, in a magnesium-base alloycasting containing aluininum and zinc as major alloying elements, analuminum, magnesium, and Zinc compound iis concentrated in scatteredareas at the grain boundaries, and that, when the casting is given thesolution heat treatment, this scattered AlXMgyZnZ compound passes intosolid solution. When this solution is aged by the known processesabove-mentioned, viz., heating at sixteen hours at 350 F., the`consequent pearlitic precipitation or" the aluminummagnesium-Zinccompound is a coarse formation produced by a comparatively rapid action.During the preliminary aging period, namely, about three (3) hoursheating at 250 Fil", the aluminum-magnesium-zinc com'- po'undcomparatively slowly precipitate'sin aime pearlitic structure, andduring the later treatment for about thirteen (13) lhours at 350vnaam,.-10

the precipitation is accelerated but continues on the basis of the fineprecipitation which takes place during the earlier aging period at thelower temperature. Thus the characteristics of the final product arebettered to substantially the respective amounts hereinbefore mentioned.The improvements are noted in the other specific procedures described.

A microscopic examination of the test bars has been made.Solution-heat-treated magnesiuin alloy consists of uniform solidsolution crystals with some heterogeneous phases (MgzSiMn.) both at thegrain boundaries and within the grain. The structure of all commerciallyusable aged condition metal consists of '75 to 50% of apparentlyretained solid solution crystals and 25 to 50% precipitated areas,similar in appearance to pearlite in steel. Such grain structure is inagreement with X-ray investigation which indicates that during aging anincreasing portion of the solid solution decomposes (almost) to itsequilibrium condition while the remainder is subject to a very slowprecipitation process. The completely precipitated material apparentlyhas only minor commercial significance because it possesses both lowertensile strength and elongation than the intermediate stages, althoughpossibly associated with a higher yield strength. The microstructure ofthe partially (and completely) precipitated conditions when aged at thesame temperature throughout the entire aging period is distinctlydifferent for different aging temperatures. The lamellae in theprecipitated areas are thinner' and closer together the lower the agingtemperature. And at lower aging temperatures the aging time appears tobe of little iniiuence in this regard. At the higher aging temperatures,comparatively long periods of aging time result in some breaking up andcoagulation of the lamellae.

The microstructure of the bars subjected to the improved stepped agingalso exhibits distinctly nner lamellae than that of metal aged duringthe entire aging period at the higher of the two temperatures used inthe stepped aging. To this distinctly finer lamellar precipitate isattributed the superior physical properties of the product obtained bystepped aging. stepped aging results in a structure and .in propertiesvery similar to those obtained over a considerably longer 'period 'by anaging at a single temperature intermediate the two temperatures of thetwo stages of stepped aging. Hence, a major benefit derived from steppedaging is a reduction in aging time.

What I claim is:

l. The process of improving the ultimate strength, hardness, andelongation characteristics of a magnesium-base alloy, consisting insolution-heat-treating a casting thereof, containing a proportion ofaluminum of from about 6% to about 9%, and a proportion of Zinc inpercentage of from about one-half to about one-nfth the percentage ofaluminum, substantially all of the remainder being magnesium, thesolution heat treatment including a quenching; then aging the alloy, byheat treatment thereof at 250 F. and continued heat treatment thereof at350 2. The process of improving the ultimate strength, hardness, andelongation characteristics `of a magnesium-base alloy, consisting insolutionheat-treating a casting thereof, containing a proportion oraluminum of from about 6% toabout 9%, and a proportion of zinc inpercentage of from about one-half to about one-fth the percentage ofa1uminum,substantially all or the remainder lbeing magnesium, thesolution heat treatment including a quenching; then aging the alloy, byheat treatment thereof for approximately three hours at 250 F. andcontinued heat reatment thereof for approximately thirteen hours at 350F.

3. An aging treatment to improve the ultimate strength, hardness, andelongation characteristics of a magnesium-base alloy, a casting ofwhichhas been solution-heat-treated and air-quenched, said castinghaving from 6 to 9% aluminum and 2 to 3% zinc, substantially all of theremainder being magnesium, consisting in rst heating such alloy at from235 F. to 265 F., and then continuing the heat treatment at from 340 F.to 380 F.

4. An aging treatment to improve the ultimate strength, hardness, andelongation characteristics of a magnesium-base alloy, a casting oi whichhas been solution-heat-treated and airquenched, said casting having from6 to 9% aluminum and 2 to 3 zinc, substantially 0.15 manganese, theremainder being magnesium, consisting in first heating such alloy forapproximately three hours at from 235 F. to 265 F., and then continuingthe heat treatment for approximately thirteen hours' at from 340 F. to380 5. improvements in treating a magnesium-base alloy containing from 6to 9% aluminum,` from 2 to 3% Zinc, substantially all of the remainderbeing magnesium, consisting in solution-heattreating a casting of suchalloy, including an air-quench; then aging the alloy by heat treatmentthereof for approximately three hours at from 235 F. to 265 F.;continuing the heat treat ment for approximately thirteen hours at from340 F. to 330 F.; and then air-cooling at and to room temperature.

6. Improvements in treating a magnesiumbase alloy containing from 6 to9% aluminum, from 2 to 3% zinc, substantially all of the remainder beingmagnesium, consisting in solution-heat-treating a casting of such alloy,including quenching thereof; then aging the alloy by heating it at from235 F. to 265 F. to elect comparatively slow precipitation of analuminum-magnesium-zinc compound having a fine pearlitic structure, andthen continuing the heat treatment at a higher temperature to accelerateprecipitation.

7. A magnesium-base alloy produced by a 2- stage aging treatmentconsisting in first heating a solution-heat-treated and quenched castingcontaining 6 to 9% aluminum and 2 to 3% zinc, substantially all of theremainder being magnesium, at from 235 F. to 265 F. for a substantialportion oi the entire aging period, and then continuing the heattreatment at from 340 F. to 380 F., the alloy being characterized byimproved ultimate strength, hardness, and elongation, as compared withalloys aged for substantially the same period of total aging time at thehigher temperature of the 2-stage aging.

8. A magnesium-base alloy produced by a 2- stage aging treatmentconsisting in first heating a solution-heat-treated and quenched castingcontaining substantially 6% aluminum and substantially 3% zinc,substantially all of the remainder being magnesium, at from 235 F. to265 and then continuing the heat treatment at from 340 F. to 380 F., thealloy being charackterized by. precipitated aluminum-magnesiumzinccompound having a fine pearlitic structure imparting thereto improvedultimate strength, hardness, and elongation.

fganese;.thesremainderibing'magnesium, at from AV235to.;265iFOraaiSubStantial A.portion 'of `the'entire:agingiperiodeandizthen ,continuing the heat treatment at from340 F. to 3380F., the alloy being `characterized cby .improved ultimate..A:str.en.:th,` hardness, iandifelongation, dasV compared "withrralloysiagel uzfor 1 substantially vthe same perriodiofltotal:againgttime;` .atthe higher temperatureroff thef2estage aging.

.11. .n magnesium-:base alloy u producedby `a 2- stage-agin'g-treatmentnconsisting in first heatling v a:slolution-heatetreated and i quenched casti ingrcontainingfsubstantiallyi -alumintmfi, `sub- `:stantiallyfZ zinc,andlsubstantially 0.15% man- ;ganesathe remainderzbeingfmagnesium, atfromv 235 F. to 265 F. for a substantial portion of fthe .1 entire-agingperiod, and fthen continuing the heat treatment atffromi'liilbli to 380?the -alicy `.being characterized 'by improved `ultimate strength;hardness, f1 and elongation, as compared`Withalloys.iagedfortsubstantially the same period of l total agingiti-mo fat fthe Ahigher temperature ofitheT2-stage--aging-12.1Improvements' in itreating a magnesiumbase alloy-'containingfiromito9%` aluminum, `from"2 to 31% 4tiin'c,-substsultiallyfall `oftheremaindenbeing magnesium,consisting in solution- 'heat-treating fa'casting-of such alloy, including quenching-thereof;ftheniaging the-alloyby heatinglit iatrabout`250iF-ito e'iiectpornparativelyslowprecipitation #of an aluminum-magnesium-zinc compoun'dh' ing1a'peailiti-c' structure, and then ncontiniiin-g'g the; heat"V treatment'at about 350 F. to accelerate Mprecipitation fthe heatitreatment atabout 250 F. being 'f'or a substantial portion yof theAi entiI-'efheat-treating period.

` lf3. AAfinanganeserbase:alloyJ produced `by a 2- stageagingtreatmentrconsisting in heating a .eolution-heatiti-eated'andYquenched casting con- "tainingf to'-9 %faluininum` and i2* to 3 zinc,subetantially' allffof'- the remainder Abeing magnesium, foverejtotalheatingrperiodoffromfour to eight hours.wrst at from 225 F. to 275"'F.for a subrtantialT portioniofthe Aentire heating period but notexceeding fone-half ;of:the1"total time, and then continuing the heattreatment for the balance of the heating period at from 340 F. to 400the alloy being characterized by precipitated aluminum-magnesium-zinccompound having a ne pearlitic structure imparting thereto an improvedcombination of properties over those of similar alloys heated for asubstantially longer total heating period at the temperature at whichthe second of the above-mentioned heat treatments is effected.

14. An aging treatment to improve the ultimate strength, hardness, andelongation characteristics of a magnesium-base alloy, a casting of whichhas been solution-heat-treated.and airquenchedsaidcast-ing.ltiavngiromhV to 9% aluminum and 2 to 3% .-zinc,substantially0.15% manganese,.the remainderbeing magnesium, consisting in rstheatingsuchalloy for-approximately three hours at about 250? F.,.andthencontinuing the heat treatment forapproximately thirteen `hours at about350. F.

l5. An improvement in agingcommercial magnesium castingA alloys.comprised ci from 5.3 `to 0.7% aluminum, from..2.5 to 3.5% zinc,aminimum of 0.15% manganese, and a .maximum of 0.30% silicon, thebalance being magnesium, consisting in heating the`solution-heat-treated vcondition thereofiromfaboutene to about one andone-half hours at from225F..to275 F., and` then stepping-up the `heating`temperature to from about 375 F. to about 400F. and continuing theheating at thestepped-uptemperaturefor from about two and. one-halflhours tovabout three hours.

16. An improvementin aging commercial magnesium casting alloys comprisedof'from y5.3to 6.7% aluminum, fromi2.i5to 3.5% zinc,-a minimum of 0.15%manganese, andra maximum of 0.30% silicon,` the balance being.magnesium, consisting in continuouslyiheating the solution-heattreatedcondition thereof at two stepped temperatures of about 250:F.-and.400.F., respectively, for a total periodv ofabout.four.-hours,.of whichthe initial heating atV about 250.F.,-is from about one to about one andone-half hours.

17. An improvementin aging `commercial magnesiumcasting'alloysccomprised-of from 5.3 to 6.7% aluminum, from f2.5.to 3.5%zinc, a minimum of 0.15%fmanganese,-and a-maximum of 0.30% silicon,.thebalance being magnesium, conssting in continuously. heatingrthesolution-heattreated condition thereof at twostepped temperatures ofabout 250.F.and 400'F.,-respectively, for a total period of about fourhours, ofwhich the initial heating at.250 F. is about one hour.

18. A magnesium-base alloy produced by Van aging treatment4lconsistingin` continuously heating a solution-heat-treated castingcontaining from 6 to 9% a1uminum,.from2 to 3% zinc, about 0.15%manganese,` the balance-being magnesium, at two stepped temperaturesoffabout 250 F. and from about 340F: toabout -380:F., respectively, inwhich the initial lower heating'tempe-rature at about 250 F. isutilized` everasubstantial portion of the entire heating period butnotexceeding one-half of the totaltimegthe falloy being `characterizedby an improved combination of` properties over those of similar ffalloysheated for the Whole period at thehghertemperature of the steppedtemperatures.

19. A magnesium-basera'lloy produced by an aging treatmentconsistngintfirst heating a solution-heat-:treated:casting :containingfrom 5.3 to 6.7% 'aluminumgfrom 2.5:.to 3.51% zinc, ay minimum `ci 0.15%s.manganese,` andea i maximum of 0.30%silicon;:the'balance'beingxmagnesium for from one to one and one-halfhours at atemperature of from about 225 F. to 275 F. and thenstepping-up the heating temperature to from 375 to 400 F. and continuingthe heating at the stepped-up temperature for from tWo and onehalf tothree hours, the alloy being characterized by a structure andcombination of properties comparable to those of similar alloys aged bystandard commercial practice, viz., for periods materially longer thanfour hours and at a single temperature intermediate 225 F. and 400 F.

20. A magnesium-base alloy produced by an aging treatmentV consisting incontinuously heating Va Vsolution-heat-treated casting containing from5.3 to 6.7 aluminum, from 2.5 to 3i5% zinc, a minimum of 0.15%manganese, and a maximum of 0.30% silicon, the balance being magnesium,for about four Vhours total time at two stepped temperatures orf; about250 F. and 400 Fg respectively, in which: the lower heating temperatureis utilized over a period of about one and one-half hours, thealloy'being characterized by markedly increased elongation, ascomparedwith that of a similar alloy aged by a single conventional temperatureheating at abc-ut 350 F. over a period of sixteen hours.

21. A process of aging commercial magnesium casting alloys consisting inheating the solutionheat-treated condition'of a casting thereoiVcontaining a proportion ot aluminum of from about 6% to about 9%, and aproportion of zinc of from about 3%: to 2%, substantially all of theremainder being;V magnesium, at stepped-up temperatures, viz., rst offrom about 235 F. to about 265 F., and then of from about 340 F. toabout 380F., the first-mentioned heating in the temperature range offrom about 235 F. to about 265 F. being utilized over a substantialproportion of the entire heating period but not exceeding one-half thetotal aging time, the aged alloys being characterized byan improvedcombination of properties over those of similar alloys heated forthewhole period at a single'temperature within the range of Vfrom aboutY235 F. to about 380 F. if i 22. A process ofaging commercial magnesiumcasting alloys consisting in heating the solutionheat-treated conditionof a casting thereof containing a proportion of aluminum of from about6% to about 9%, and a proportion of zinc of from about 3% to 2%,substantially all of the remainder being magnesium, at stepped-uptemperatures, viz. rst ofabout 250 F., and then of from about 350 F. toabout 400 F., the total aging Vtime being about four-hours, and thefirst-mentioned heating of about 2507F. being from about 25% to about371/2 of the total aging time.

23. A process of aging commercial magnesium casting alloysfconsisting inheating the solutionheat-treated condition of a casting thereofcontaining from 5.3% to` 6.7% aluminum, from 2.5% to 3.5% zinc, aminimum of .15% manganese, and a maximum of 0.30% silicon, substantiallyall of the remainder being magnesium, at stepped-up temperatures;viz.,first ofr about 250 F., and then of from about-350 F. to about 400 FL,the total agingftime being about four hours, and the firstmentionedheating of about 250 F. being from about 25% to about 37%, of the totalaging time.

24. A process of aging commercial magnesium casting alloys consisting inheating the solutionheat-treated conditionof a casting thereofcontaining a` proportion of aluminum of from about 6% to about 9%, and aproportion of zinc of from about 3% to 2%, substantially all of theremainder being magnesium, at stepped-up temperatures, Viz., first ofabout 250 F.; and then of about 375 F., the total aging time being aboutfour hours, and theV first-mentioned heating of about 250F. being not toexceed two hours.

25. A magnesium-base alloy containing from about 6% to about 9%aluminum, and from about 3% to 2% zinc, substantially all of theremainder being magnesium, produced by an aging treatment consisting inheating a solution-heattreated casting thereof for from about four hoursto about eight hours total time at steppedup temperatures, viz., rst offrom about 225 F. to about 275 F., and then of from about 350 F. toabout 400 F., in which the first-mentioned heating inthe temperaturerange of from about 225 F. to about 275 F. is utilized over a period notexceeding one-half of the total aging time, the alloy Vbeingcharacterized by an improved combination of properties over those ofsimilar alloys heated for the whole period at a single temperatureWithin the range of from about 225 F.'to about 400 F. Y V

26. A magnesium-base alloy containing from about 6% to about 9%aluminum, andffrom about 3% to 2% zinc, substantially all of theremainder being magnesium, produced by an aging treatment consisting inheating a solutionheat-treated casting thereof at stepped-uptemperatures, Viz., rst of about 250 and then of from about 350 F. toabout 400 F., the total aging time being about four hours, and theiirstmentioned heating of about 250 F. being from about 25% to about371/2% of the total aging time.

27. A magnesium-base alloy containing from 5.3% to 6.7% aluminum, from2.5% to 3.5% zinc, a minimum oi .15% manganese, and a maxi-mum of 0.30%silicon, substantially all of the remainder being magnesium,r producedby an aging treatment consisting in heating a solutionheat-treatedcasting thereof at stepped-up temperatureaviz., rst of about 250 F., andthen of about 375 F., the total aging time being about four hours, andthe rst-mentioned heating of about 250 F. being for about one hour. t,

n28. A magnesium-base alloy containingfrom 5.3% to 6.7% aluminum, from2.5% to:3.5% zinc, a minimum of .15% manganese, and a'maximum of 0.30%silicon, substantially 'all of the remainder being magnesium, producedby an aging treatment consisting inheating a solutionheat-treatedcasting thereof, at stepped-up temperatures, viz., irst of about 250YF., and then of about 400 F., the total aging time being about fourhours, and the first-.mentioned heating of about 250 F. being foraboutone hour, the alloy being characterized by increased yield strengthand elongation with no substantial loss in tensile strength as comparedwith similar alloys aged at a single temperature of about 350 F. forabout sixteen hours.

EDWARD J. VARGO.

No references cited.

Certificate of Correction Patent No. 2,477,508 July 26, 1949 EDWARD J.VARGO It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfellows:

Co1umn"35\,1ine 13, for the syllables and hyphen speciieareadspecification; 9, line 25, for againg read aging; line 54, for the Wordsmanganese-base read magnesium-base;

and that the said Letters Patent should be read With these correctionstherein that the same may conform to the record of the ease in thePatent Oice.

Signed and sealed this 20th day of December, A. D, 1949.

THOMAS F. MURPHY,

Assistant Uommssz'oner of Patents.

